The name Alenquer is said to derive from the germanic "Alen Ker" meaning the Temple of the Alans, and the city itself is, legend says, is said to have been established by the Alanian king Attaces. The Alans' dog, the Alaunt, is represented in the city's coat of arms. This is nothing but a legend, though, as there have been settlemenst in the area before Roman times, and these were also established there, namely in the location of Ierabriga or Lerabriga. The city's castle, however, may have been established by the Alans, or maybe the Visigoths.

Alenquer recived it's Foral in 1212 by the hand of Infanta Sancha, Lady of Alenquer, daughter of King Sancho I of Portugal.